280 On the Condensation of Steam upon Cold Surfaces. [May 1, 



The point of no air might have been chosen as the point in which the 

 curves should coincide ; but, as has been previously explained, the results 

 under such circumstances are to be taken as indicating the power of the 

 condenser to carry off the heat. Had it been possible to keep the 

 condenser cool, then there is reason to believe that there would have been 

 no limit to the condensation of pure steam, and that the true form of the 

 curves is like that shown by the dots. 



Ratio of the pressure of air to that of steam. 



Although the curves do not coincide, yet they are all of the same form, 

 and the difference between them is not greater than can be accounted for 

 by the disturbing causes already mentioned. They all show that the 

 effect of air begins to fall off rapidly when its pressure amounts to one- 

 tenth that of the steam, and that when it amounts to about one fourth 

 that of the steam the admission of more air produces scarcely any effect. 



14. Conclusions. — The conclusions to be drawn from these experi- 

 ments are as follows : — 



1. That a small quantity of air in steam does very much retard its 

 condensation upon a cold surface ; that, in fact, there is no limit to the 

 rate at which pure steam will condense but the power of the surface to 

 carry off the heat. 



2.That the rate of condensation diminishes rapidly and nearly 



